1. Field of the Invention
The present invention relates generally to the field of tube strengthening. More particularly, the present invention relates to a reinforcing liner for use in pipe rehabilitation, wherein the liner is saturated with curable resin, introduced into a tube or pipe, shaped to conformingly line the pipe, and cured in place so as to form a rigid liner.
2. Discussion of Related Art
Various methods of rehabilitating a tube, such as a pipe that is buried underground, are known in the art. Generally speaking, such methods include the use of a liner having a diameter that is substantially the same as the inner diameter of the pipe to be rehabilitated. The liner frequently includes an impermeable layer and an adjacent resin-absorbing layer. This resin-absorbing layer is soaked with a liquid resin prior to the introduction of the liner into the pipe. After being properly positioned in the pipe, the liner is pressed against the inner surface of the pipe by fluid pressure.
Most liners in such applications utilize a layer of nonwoven felt for the resin-absorbing layer of the liner. One of the purposes of the felt is to provide support for the uncured resin of the impregnated liner. The felt serves as a reservoir and/or carrier means for the uncured resin. Once cured, the resin provides the structural strength of the liner.
These so-called cured-in-place liners are typically installed in environments that are continuously exposed to water and other corrosive materials. Cured-in-place liners are also exposed to varying temperatures and flow conditions.
The below-referenced U.S. patents disclose embodiments that were at least in part satisfactory for the purposes for which they were intended. The disclosures of all of the prior United States patents discussed herein are hereby expressly incorporated by reference into the present application in their entireties for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
Wood's U.S. Pat. No. 4,390,574 discloses an inversion (called eversion) liner that is strengthened by blowing chopped glass fibers onto the web prior to a needling stage. The needling “entangles” the chopped glass fibers with the fibers of the web.
Wood's U.S. Pat. No. 4,836,715 also discloses a liner. However, this later Wood patent generally discusses with disfavor liners having polyester fibers extending orthogonally to the plane of the liner material caused by needling. According to Wood, the tensile strength of a liner is negatively impacted by fibers orientated this way. Thus, this Wood patent attempts to solve this by adding layers of reinforcing fibers, including glass, orientated in a circumferential direction.
U.S. Pat. No. 4,902,215 and U.S. Pat. No. 5,052,906, issued to William H. Seemann, address the use of a flow medium fed by a “pervious conduit” (a resin feed or channel) communicating with the flow medium, to combine use of core materials with resin flow features and reusable vacuum bags with integral resin feeds and distribution networks.
Kittson et al. U.S. Pat. Nos. 5,836,357 (and divisionals 5,873,391, 5,911,246, and 5,931,199) discloses an inversion liner constructed of several layers of materials. Two of these layers contain chopped glass fibers. The glass fibers are stitched or sewn onto a polyester felt and are randomly orientated in an x-y plane.
The prior art as described in U.S. Pat. Nos. 5,240,533, 5,480,697, and 6,037,035 demonstrates an “integrated sandwich structure”. The patents generally provide for a means of manufacturing (weaving) the “integrated sandwich structure” so as to optimize the structure's ability to maintain x and y fiber plane separation during composite processing.
Smith's U.S. Pat. Nos. 6,708,729 and 6,932,116 disclose a reinforced liner consisting of several layers, one of which includes reinforced fibers, preferably carbon or glass. It is further disclosed that these fibers may be arranged in one axis, in one plane or randomly in all three axes, such as with standard felt. However, the preferred alignment is circumferential.
Woolstencroft et al.'s U.S. Pat. Nos. 6,837,273 and 7,096,890 disclose the use of chopped glass fibers mechanically bonded to a flexible felt layer. The fibers can be bonded to the flexible layer by a light needling process that keeps the majority of glass fibers “properly” orientated, i.e., in the x-y plane.
Mack et al.'s U.S. Pat. Nos. 7,060,156 and 7,048,985 disclose a three-dimensional “spacer” fabric for laminates and discusses various “z direction” reinforcing fibers that can be used including glass fibers.
Many of these previously recognized solutions have the disadvantage of being not completely effective and having a relatively high cost. Further, in many instances of cured-in-place pipelining, the final product fails to meet the required ASTM standards. If these standards are not met, then catastrophic failure of the liner is possible due to the external buckling pressure exerted by the hydrostatic load and soil compaction or lack of compaction.
In some cases, point load failure is probable because the liner's cross sectional thickness is increased too much. This reduces the internal diameter of the host pipe which can result in loss of hydraulic capacity. Where point loading is not a problem, the amount of head pressure used to install a typical liner oftentimes compresses the cross sectional thickness below an acceptable level as determined by the ASTM standards for cured-in-place pipe.
Also, underground pipes, especially failing or nearly failing underground pipes, can present an extremely harsh use environment for rehabilitating liners. Failing or nearly failing underground pipes can be subject to, e.g., exposure to moisture or wet material flow, fungi, microbial and other organism influences, aerobic and/or anaerobic conditions, acid and/or basic conditions, and/or other extreme environmental conditions. Numerous resins are ill suited for prolonged exposure to such harsh use environments. Correspondingly, such numerous known resins cannot be used during pipe rehabilitation because they afford unacceptably short duration use lives.
Furthermore, many resins can pose unacceptable contamination risks to the contents flowing through the pipes. Other resins can pose potential threats to, e.g., the environment during installation and use. For example, numerous known risks are associated with resins that are solvent based. Most solvent based resins and other resins include or contain a variety of hazardous air pollutants (HAPs), various volatile organic compounds (VOCs), all of which can be damaging to the environment and/or individuals exposed to such HAPs and VOCs.
What is needed therefore is an invertible liner that may be used with the smaller diameter tubes. What is further needed is a liner that insures that ASTM standards are consistently met without dramatically increasing the cost of the finished product. What is also needed is a liner that has a flexible, three-dimensional weave or knit design. What is also needed is a system with installation processes that are similar to current processes so that installers do not need to be retrained. What is also needed is a system that incorporates resins that do not compromise the integrity of the constituents flowing through rehabilitated pipes and provide suitable use lives before requiring repair or subsequent rehabilitation. Furthermore, pipe rehabilitation systems are needed that utilize resins with few or no HAPs and/or VOCs.